Santiago Alvarez claimed that, according to the West-German trial verdict against Heinz Rie., there were "only" six hearsay witnesses on a homicidal gas van used by the Secret Field Police in Mogilev (GFP 570) and that the "story sounds more like a rumor than an established fact". However, as pointed out in the original posting, the verdict actually cited three eyewitnesses and five hearsay witnesses - all members of GFP 570 - on the operation of the gas van. Now, according to a report by West-German
investigators, there is in fact much more evidence on the existence and operation of this vehicle available.

This report ("partial order to dismiss the case") of 15 August 1972 (BArch, B 162 / 29269, p. 74 ff.) also quotes from interrogations of former GFP 570 members:

I have seen a truck on the yard and knew it was a so called gas wagon...When Rie. told me that I had to drive with the vehicle, I immediately knew what this was about."

"He [Se.] had the order to drive with a Secret Police secretary in a car behind the gas wagon, but not with a responsible or supervising function for this gassing trip....After the unloading of the Russians killed with exhaust, he and the Secret Police secretary continued their drive to Mogilev."

According to the document, the West-German investigators had obtained at least twenty five affirmative
testimonies from former GFP 570 staff on the gassing vehicle, thereof nine eyewitnesses on the operation of the gas van, another five on its
construction and seven hearsay on the operation of the vehicle. The
remaining four testified that the gas van was employed in Mogilev, but the
nature (hearsay or eyewitness) of the testimony is unclear from the
file. Three witnesses of GFP 570 testified that the homicidal gas van
was based on a 1.5 - 2 tons
Ford chassis captured from the Russians - thus likely equipped with a
gasoline engine, which can produce lethal concentrations of carbon
monoxide.

Even further evidence for the GFP 570 gas van can be found in the files of the East-German investigation against GFP 570 member Herbert Paland. According to Gerlach, Kalkulierte Morde, 2012, p. 766, at least two witnesses testified on the gas van and one more according to Geßner, Geheime Feldpolizei, p. 251.